This project is investigating and characterizing the capability of platinum anticancer drugs (platinum coordination complexes) to potentiate the effect of ionizing radiation on mammalian cells and animal tumors. Results obtained in this study indicate that it should be possible to extend the potentiation of damage between the two modalities to tumor cells, confirming a suggestion presented originally by Richmond and Powers based on results obtained in a bacterial system. One objective of this study is to examine the action of a variety of platinum compounds on mammalian cells in culture when used alone or in combination with ionizing radiation. Three cell lines are being used, a mouse mammary adenocarcinoma, MTG-B, a Chinese hamster lung fibroblast, V-79, and a rat brain tumor, RBT. The cells are treated under various growth conditions, and in the presence and absence of oxygen using a special gassing apparatus for the production of chronically hypoxic cells. A second objective is to test for radiosensitization of hypoxic tumor cells treated in situ. Survival of the transplantable MTG-B cells is being assayed following combined therapy using the tumor latency assay in C3H mice. Therapeutic potentiation is being evaluated using the combined platinum-radiation in MTG-B and intracerebral RBT in rats. Results of these studies should identify radiosensitizers and treatment conditions that should improve clinical tumor response to radiation therapy.